(a) Field of the Invention
This disclosure relates to negative-electrode active material for a lithium secondary battery, and a method of preparing the same. More particularly, this disclosure relates to negative-electrode active material for a lithium secondary battery exhibiting excellent capacity property and cycle life property, a method of preparing the same, and a lithium secondary battery using the negative-electrode active material.
(b) Description of the Related Art
A battery generates electric power using material capable of electrochemical reactions in a positive- and a negative-electrode. A representative example of the battery is a lithium secondary battery which generates electrical energy by chemical potential change when lithium ions are intercalated/deintercalated in a positive- and a negative-electrode.
The lithium secondary battery is prepared by using material capable of reversible intercalation/deintercalation of lithium ions as positive- and negative-electrode active material, and filling organic electrolyte or polymer electrolyte between the positive- and negative-electrode.
As positive-electrode active material of a lithium secondary battery, a lithium complex metal compound is used, and for example, complex metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, and the like are studied.
As negative-electrode active material of a lithium secondary battery, graphite capable of intercalation/deintercalation of lithium is representatively applied. However, since an electrode using the graphite has low charge capacity of 365 mAh/g (theoretical value: 372 mAh/g), there has been a limit to provide a lithium secondary battery exhibiting excellent capacity property.
Thus, inorganic active material such as silicon (Si), germanium (Ge) or antimony (sb) is being studied. The inorganic active material, particularly silicon-based negative-electrode active material may exhibit very high lithium binding amount (theoretical maximum value: Li4.1Si), which corresponds to a theoretical capacity of about 4200 mAh/g.
However, the inorganic negative-electrode active material such as silicon-based negative-electrode active material causes considerable volume change at intercalation/deintercalation of lithium, i.e., charge/discharge of a battery, and thus, pulverization may occur. As a result, pulverized particle may be aggregated, and thus, negative-electrode active material may be electrically deintercalated from a current collector, which may cause loss of reversible capacity during a long cycle. For example, the capacity of a lithium secondary battery using silicon-based negative-electrode active material may become similar to the capacity of a battery using graphite after about 12 cycles. For this reason, a lithium secondary battery including previously known inorganic negative-electrode active material, for example, silicon-base negative-electrode active material, has disadvantages of low cycle life property and capacity retention ratio, despite of advantages according to high charge capacity.
To overcome these problems, there has been an attempt to use a complex of carbon and silicon-based nanoparticles as negative-electrode active material. However, this negative-electrode active material also exhibits relatively high loss of reversible capacity during a long cycle, and thus, insufficient cycle life property and capacity retention ratio. And, capacity property is not sufficient due to a substantial content of carbon included in the nanocomplex